Failing u-values after upgrade

[ecoboost]

More problems with the IES version of SBEM. I sent a model to a colleague who has the latest version of the software. Running the model in my version yesterday the floor u-value on the compliance document was 0.23 but running his updated version this morning it is now 0.28 and failing... How can this be!? We haven't changed anything, just ran the simulation.

[ecoboost]

Just noticed the BER has changed too. Increased from 23.5 to 29.6! This is a huge difference! We really haven't changed anything, why does your software hate me!

[Complex Potential]

Sorry... how did you send your colleague the model? Did you archive it by any chance?

[Terence]

I think this is related to a recent change that was made for VE 2013 Feature Pack 1. It was documented in the release notes but I know some people don't bother reading them... See the following post in announcements

Unheated Adjoining Space adjacency written to SBEM [ID-59071]: When a room is adjacent to an unconditioned room
(including one where System is set to None) then the adjacency condition for the surface between the two rooms is
passed to the SBEM input file as ‘unheated adjoining space’ as specified in the SBEM dictionary for this kind of surface
type (For constructions separating the considered zone from an unheated adjoining space, other than meant under
‘Strongly ventilated spaces’.). This affects the way SBEM thermally treats the adjacency as well as how it assesses the
Constructions between the spaces for the purposes of Criterion 2 classification, further details are available from the BRE SBEM documentation available from BRE.

In VE 2013 Hotfix 2, if a heated space was adjacent to a space with room type 'Internal void or Warm Roof' we would write out the adjacency as 'Conditioned adjoining space'. In VE 2013 Feature Pack 1 the software now writes the adjacency as “Unheated adjoining space”.

This has repercussions for users who set the HVAC system for spaces labelled as 'Heated or Occupied' in their model to 'None'. Doing this causes the construction elements of the (now unconditioned) space to be ignored. Instead SBEM will look at what it considers to be the nearest 'Conditioned adjoining space'. This can result in a situation where you have an internal ceiling being checked against the limiting U-value for a roof for Criterion 2.

Most of the time I find that if a space has a HVAC system set to 'None' then the space usually has an activity that requires no heating (cupboard, plant room etc..). In this case it is probably best assigning an HVAC System to the space as the Heating schedules for these activities in SBEM will be set to 'Off Continuously'.
Doing this means the adjacency will be treated in the correct manner, you won’t see any increase in heating energy consumption and the U-value check will be carried out at the correct level for the space. If the spaces are indirectly heated from an adjacent space then the guidance states they should also be assigned the heating system of the adjacent space providing the heating.

Also, it is worth pointing out, for the purposes of an SBEM analysis void spaces should not be modelled directly. Instead they should be absorbed into the adjacent conditioned space and the U-value adjusted accordingly. For more guidance on this i'd recommend reading the iSBEM user guide on the BRE website

[ecoboost]

Thanks. It is a bit unfair that we need to do a lot of work on a project we were close to finishing. This also re-iterates my point I made on you not having proper guidance available in the user guides.

[jerry]

Lucky you, ecoboost, my BER has jumped from 34.5 to 50.3 for exactly the same reason. All because some assessors insist on drawing ceiling voids as separate zones and labelling them as "warm roof", even though this contradicts the SBEM guidance. I now refuse to accept models drawn by other assessors as there is usually too much work involved in correcting them.

[jerry]

Terence - given these changes in the conventions, what's your recommendation for "fixing" an older model where ceiling voids have been drawn and labelled as warm roofs ? 1) insert holes into all the void floors, 2) merge each void with the zone beneath, 3) set the "associated occupied room" for every void, 4) something else ? It seems to me that whatever option is followed, it's going to take a while…….

Jerry

[ecoboost]

We just re-drew the model with the following guidance

Occupied spaces not directly heated were drawn and assigned the heating system of the adjacent heated space
Unheated spaces were absorbed into adjacent conditioned zones
Voids were absorbed into adjacent conditioned spaces
Unheated roof spaces were not modelled. The ceiling of the heated space below was assigned a roof construction with the u-value adjusted

I'm hoping this is now correct!

[Terence]

Jerry, I would recommend merging the two spaces but connecting with a 100% hole will also give the same result.

[jerry]

Most of the time I find that if a space has a HVAC system set to 'None' then the space usually has an activity that requires no heating (cupboard, plant room etc..). In this case it is probably best assigning an HVAC System to the space as the Heating schedules for these activities in SBEM will be set to 'Off Continuously'.
Doing this means the adjacency will be treated in the correct manner, you won’t see any increase in heating energy consumption and the U-value check will be carried out at the correct level for the space. If the spaces are indirectly heated from an adjacent space then the guidance states they should also be assigned the heating system of the adjacent space providing the heating.

Terence, while this does overcome the Criteria 2 issue, the SBEM guidance states that such rooms should not be set in this way:

"On the other hand, if a zone is unheated and totally enclosed thus heated air cannot freely move from a heated zone into it, such as a plant room, a store, or a toilet, you are advised to define it in iSBEM as "Zones without HVAC" "
(p.142)

Jerry